The present invention relates generally to hydraulically-actuated system, and more particularly to a electro-hydraulic closed loop actuator of a variable delivery fixed displacement pump.
U.S. Pat. No. 6,035,828 to Anderson et al. describes a variable delivery actuating fluid pump for a hydraulically-actuated fuel injection system. In this system, a high pressure rail supplies pressurized lubricating oil to a plurality of hydraulically-actuated fuel injectors mounted in a diesel engine. The high pressure rail is pressurized by a variable delivery fixed displacement type pump that is driven directly by the engine. Pump pressure control is provided by hydraulically varying the high pressure output of the pump. This is accomplished by providing a piston arrangement in the pump that incorporates a moveable sleeve on the outside of the pistons. Depending upon the position of the sleeve, a spill port on the piston is opened or closed. When the spill port is opened, the fluid is spilled back into the low pressure side of the pump, instead of being pushed into the high pressure rail. The position of the sleeve is maintained by a hydraulic actuator. Fluid in the hydraulic actuator moves an actuator shaft, which in turn moves the sleeve.
While the Anderson et al. hydraulically-actuated system using a variable delivery pump performs better than previous systems there remains room for improvement. The complicated mechanical structure of the pump and hydraulic actuator provides potential leak paths for hydraulic fluid. Also, because the viscosity of lubricating oil varies due to temperature, control of the pump may be sluggish when the oil is of an extremely cold temperature.
The present invention is directed to overcoming problems associated with, and improving upon, hydraulically-actuated systems of the prior art.
In one aspect of the invention a variable delivery fixed displacement pump is provided. The pump includes an actuator having an actuator bore, a first directional port and a second directional port. An actuator shaft is disposed within the bore and moveable in a first direction and a second direction in response to receiving fluid from the first or second directional port. The actuator shaft is adapted to vary the amount of fluid output from the pump. A valve having a spool, a first solenoid coil and a second solenoid coil directs fluid to one of the first or second directional ports in response to a signal from a controller.
In another aspect of the invention a fluid delivery system is provided. The fluid delivery system includes a controller, a pump having a high pressure outlet and an actuator having a position sensor. A pressure sensor is provided to sense the pressure in a high pressure rail is included. A valve between the high pressure outlet and one of the first or second directional ports, directs fluid to he actuator.
In yet another aspect of the present invention a method for controlling a variable delivery fixed displacement is provided. The method includes delivering a flow to one of a first or second directional port. An actuator shaft is moved in one of a first direction and a second direction in response to delivering flow to one of the first and second directional flows. Fluid flow from the pump is varied depending upon position of the actuator shaft.